This invention relates to a vertical type multi-cylinder engine and more particularly to an improved system for improving the running characteristics and exhaust emission of such an engine.
As is well known, there is considerable effort to reduce the undesirable exhaust emissions of internal combustion engines. In certain particular types of applications, the effective exhaust emission control is quite difficult. One example of such an application is an outboard motor. Because of its extremely compact nature, it is very difficult to effectively treat the exhaust gases in the engine of an outboard motor.
Conventionally, the cylinders of the engine are disposed in a horizontal orientation so as to drive a vertically disposed crankshaft. The exhaust gases are conveyed from the cylinders of the engine downwardly by an exhaust pipe into an expansion chamber in the driveshaft housing. As a result of this compact construction, the exhaust pipe must have a relatively short length and the length between the outlet end of the exhaust pipe and the lower most cylinder is quite short. This can provide significant problems in connection with efficient exhaust emission control.
These problems are further complicated by the fact that outboard motors frequently run at a condition when the engine speed is actually below idle speed. That is, it is frequently the practice to run the outboard motor in a "trolling" condition and under this condition the speed of the engine is very low. This gives rise to difficulties in obtaining good scavenging and full burning of the fuel charge, particularly with two cycle engines, the commonly used power plant for outboard motors of this type.
It is, therefore, a principal object of this invention to provide an improved arrangement for an outboard motor that will insure that the exhaust gases can be effectively treated.
It is a further object of this invention to provide an improved control system and method for operating an outboard motor so as to insure that there is a minimum of unburned hydrocarbons in the exhaust gases, particularly under the difficult trolling condition.